1. Field of the Invention
This invention relates generally to gas-operated automatic-loading firearms and more particularly to a gas pressure adjusting device of a gas-operated mechanism in an automatic-loading shotgun firing ordinary shotshells of 23/4-inch length.
More specifically, the invention relates to a gas pressure adjusting device of the above stated character which automatically adjusts the gas pressure within the actuating cylinder of the gas-operated mechanism responsive to the magnitude of the gas pressure which is generated in the bore at the time of firing of a shotshell and is introduced into the cylinder via a gas port, thereby to cause the gas-operated mechanism to always operate under the most suitable operational conditions even when the load of the shotshell is changed.
2. Description of the Related Art
In a typical automatic shotgun, as will be described more fully hereinafter, when a shotshell is fired, gas under great pressure is generated within the gun bore. A portion of this gas is tapped through a gas port and is introduced into an actuating cylinder of a gas-operated mechanism installed partly within and around a tube magazine that is parallel to and below the gun barrel. This mechanism is driven by the gas to actuate a breech bolt which undergoes a recoiling motion while compressing a recoil spring, which thereafter forces the breech bolt to undergo a counter-recoiling motion to return the breech bolt to its initial state whereat it closes the breech of the chamber. During its recoiling and counter-recoiling motions, the breech bolt carries out the actions of ejecting the empty case of the shotshell which has just been fired, loading the succeeding shotshell in the magazine into the chamber, and cocking the firing mechanism in preparation for the succeeding firing. The above described cycle of operation in a gas-operated auto-loading shotgun is widely known.
The shotshells used in an automatic shotgun operating as described above differ widely, there being not only deviations between individual shotshells but also a wide range of loads from low-base loads of the order of 28 gr to high-base loads of the order of 42 gr. In comparing a low-base load and a high-base load, a great difference exists in the firing gas pressure. Thus the gas-operated mechanism must be capable of operating positively with the gas pressures of all of the above mentioned shotshells. For this reason, in order to prevent malfunctioning with the gas pressure exerted by the minimum low-base load, the gas-operated mechanism is designed with a low-base load as a standard basis.
As a consequence, when a conventional auto-loading shotgun as described above fires a shotshell of high-base load, a tremendous gas pressure is generated, and the above described moving parts are propelled rearward with excessive velocity to produce not only an impact which can cause damage or breakage of the moving parts and shortening of their serviceable life but also a powerful firing reactive impulse, or kickback, which lowers the target scoring accuracy. This has been a problem encountered in the prior art.
A first-stage measure widely resorted to for overcoming or alleviating this difficulty comprises preparing separate barrels each exclusively for a low-base load and for a high-base load, respectively, and restricting the quantity of gas introduced into the cylinder (e.g., by changing the diameter of the gas port) thereby to adjust the gas pressure within the cylinder. Since each barrel in this method is an exclusive-use barrel, positive gas pressure adjustment is achieved. However, this method is inconvenient in that, in the case where the shotgun is fitted with a low-base load barrel, an interchangeable high-base load barrel must be carried as an accessory if there is a possibility of the shotgun being used for high-base load when hunting or target shooting. Furthermore, even when an interchangeable barrel is readily available, the shotgun lacks instantaneous responsiveness to fleeting chances or "targets of opportunity", whereby it is not desirable in actual practice.
With the aim of overcoming the inadequacy of the above described first-stage measure, there has been proposed and reduced to practical use a device comprising a pressure-regulating piston provided within the cylinder and an elastic member such as a spring or a piece of rubber for backing up the piston, which is activated to undergo forward-rearward movement in response to the magnitude of the gas pressure introduced into the cylinder to vary the internal volume of the cylinder and thereby to regulate the gas pressure, as described in the specification of Japansee Pat. No. 821390. However, while the gas pressure regulation according to this device is effective for variations of gas pressure within a limited range, it cannot cope with gas pressure variations within the entire range of gas pressures from a low-base load to a high-base load.
In order to overcome the limitation of the above described second-stage measure, devices as disclosed in U.S. Pat. Nos. 3,020,807 and 3,127,812 and that which we have practically applied to a number of automatic shotguns, as illustrated in FIG. 6 of the accompanying drawings and as described hereinafter, have been proposed as third-stage measures. In each of these third-stage devices, a pressure-adjusting valve is provided within the cylinder, and, when the gas pressure within the cylinder becomes higher than a specific pressure, the pressure-adjusting valve is activated to open the valve opening and discharge the excessive gas to the outside air, thereby adjusting the gas pressure acting in the cylinder.
For a third-stage device, in which the gas pressure within the cylinder is adjusted by discharging surplus gas to the outside by means of a pressure-adjusting valve as described above, to be fully satisfactory, it must satisfy all of the following four necessary and desired conditions.
(1) When a low-base load shotshell is fired, the device must never operate, that is, the valve body must not open the valve opening. If the valve opens and discharges gas when a low-base load shotshell is fired, the gas pressure acting on the piston will be insufficient, whereby malfunctioning of the gas-operated mechanism will occur.
(2) The operational response of the pressure-adjusting device must be prompt and positive. The time elapsing from percussion, firing, and acting of the resulting gas pressure on the piston to completion of recoiling of the breech bolt is a very short time, ordinarily being of the order of 0.02 to 0.03 second. If the gas pressure adjustment is not accomplished within an even shorter time than this, an excessive gas pressure will act on the piston, whereby one of the objects of the device will not be achieved.
(3) The masses of the moving parts of the device must be kept as small as possible. If the masses of the moving parts are large, it will become impossible to satisfy the above condition (2).
(4) The gas discharge hole or holes, i.e., the valve opening, must be made as large as possible so that the required quantity of the gas will be discharged instantaneously.
As set forth in condition (2) above, the specific quantity of gas must be discharged through the opened valve opening within a very short time, and if this is not accomplished, satisfactory pressure adjustment cannot be expected.
As will be discribed in greater detail hereinafter, the conventional gas pressure adjusting devices, even third-stage devices, in shotguns of the instant type do not fully satisfy the conditions set forth above. For example, one problem is that a great spring force is necessary, and another is that the masses of the valve body and the spring tend to be large, whereby the above conditions (2) and (3) cannot be met. Another difficulty is encountered in the structural design of a partition wall constituting the valve seat with one or more valve opening to operate cooperatively with the valve body, the difficulty being in providing sufficient mechanical strength to the partition wall, whereby the above condition (4) cannot be fully satisfied. The above mentioned large spring force further causes great difficulty in the work of assembling the related parts.